Processes for maximizing the amount of PPS produced from a given reactor are desired for purposes of gaining economic efficiency. Increasing the concentration of reactants per reactor volume offers a seemingly evident approach to maximizing PPS production. However, after the concentration of reactants employed exceeds about 0.36 moles of sulfur source per mole of polar organic compound, the molecular weight of the PPS resin significantly decreases.
The molecular weight of a PPS resin is generally determined by the melt flow rate of the resin. Extrusion rate is a specific type of melt flow rate particularly useful for characterizing phenylene sulfide polymers in the a lower molecular weight range, such as those produced without a polymerization modifier such as an alkali metal carboxylate, as disclosed in U.S. Pat. No. 3,354,129, (Nov. 21, 1967). The term extrusion rate, as used herein, refers to a flow rate measurement on molten polymer based on ASTM D1238, Procedure B-Automatically Time Flow Rate Measurement, Condition 316/0.345, using a 5 minute preheat time and an orifice having the dimensions of 0.0825.+-.0.002 inch diameter and 1.25.+-.0.002 inch length. A low value extrusion rate indicates a higher molecular weight resin, while a high value extrusion rate indicates a lower molecular weight resin.
Maintaining a sufficiently high molecular weight PPS resin is important for many of the commercial applications of the resin such as injection molding and the like. The deterioration of molecular weight associated with using reactant concentrations greater than about 0.36 moles of sulfur source per mole of polar organic compound is of a significant enough degree to change the characteristics of the resultant polymer. Therefore, increasing reactant concentrations beyond 0.36 moles of sulfur source per mole of polar organic compound has not been a method utilized for purposes of maximizing PPS production.